Modules and visibility

An ordinary source module uses a dotted identifier path. Under the selected source root, each dot becomes a path separator and the file name ends in .tpz. For example, geometry.point selects geometry/point.tpz. Its logical identity is the dotted relative path without the extension.

The entry file and the source files reached transitively through its imports form the source program.

Imports must precede every other top-level item in a file. A later import is rejected with TPZ2010.

Entry files and imported files use the same top-level statement grammar. Both admit declarations, free expressions, assignments, and loops. Binding initializers and free expressions use the ordinary effect rules. Import placement, visibility, mutability, control-flow targets, and all other context checks apply equally to both file roles. Importing a file does not add a statement-form restriction.

Resolve the complete source program before initialization. Initialize source modules serially, completing every dependency before its importer. At each step, choose the lexicographically smallest canonical logical module identity among modules whose dependencies have completed; compare identities by Unicode scalar value. Import spelling order and local aliases do not affect this order. After constant processing, execute ordinary top-level items in source order. Every module initializes exactly once per program invocation, including when multiple import paths reach it in a diamond. All importers share the same completed module state. A new program invocation, including a new host invocation of an exported function, creates fresh module state and repeats initialization.

A source import cycle, including a module importing itself, is rejected with TPZ3006 during resolution. The diagnostic identifies an import edge in the cycle. No module initialization or entry execution begins for a rejected graph. Break the cycle by moving shared declarations into a dependency or removing the back edge.

Binding initialization

If module initialization faults, abort the program invocation immediately. Do not execute remaining items in that module, initialize later modules, or start a waiting importer. Already completed effects remain visible; initialization provides no rollback. Report the original fault code and primary source location. An added initialization-context message does not change that diagnostic identity.

A namespace import binds the final path segment as its local namespace name. An explicit as alias supplies that name instead. Select a declaration with namespace.member.

A selected import binds each chosen export directly under its source name or its selection alias. Renaming the local binding preserves which source declaration it denotes. A selection list creates no namespace binding.

Omit as when an import keeps its default binding name. A namespace alias must differ from the final module-path segment; a selected alias must differ from that selected source name. An explicit alias repeating the default identifier is rejected with TPZ2009 during parsing, at the alias identifier. An alias that changes the local name remains permitted under the ordinary import visibility and collision rules.

A selection list must contain at least one name. Selected source names and resulting local names must each be unique. Violating these requirements is rejected with TPZ2011.

A namespace alias and a selection list cannot appear in the same import item. Their combination is rejected with TPZ2009.

A logical module may appear in at most one import item in an importing file. Repeating it is rejected with TPZ3017.

Prefix an otherwise valid function, let, const, type alias, enum, record, newtype, or protocol declaration with export to publish its binding. Without that prefix, the declaration remains module-private.

An exported immutable let uses an ordinary let pattern and optional type annotation. The pattern must bind at least one name; otherwise TPZ2007 rejects it during parsing. Every bound name becomes an immutable export with its module-and-name identity. Evaluate the initializer once, match the complete pattern, then install all bindings. Ordinary pattern typing, duplicate-name, and refutability checks still apply. If evaluation or matching faults, install no binding from that pattern and stop module initialization; earlier external effects remain. Check every resolved bound type for private nominal exposure. Public types are the extracted binding types, not the temporary initializer container. Module exports are published after successful initialization.

An exported let binding must be immutable. The form export let mut is rejected with TPZ3011 during resolution.

A namespace import may target a module with an empty export table. That module initializes normally and the bound namespace has no public members. Selecting a private or absent name is rejected with TPZ3009 during resolution, including when the target exports no names. Initialization does not require a dummy export or a separate import form.

A value or type selected through a namespace must name an exported declaration. The requirement applies in every context, including record field defaults. A private or absent member is rejected with TPZ3009 during resolution.

Direct replacement of a selected imported binding, including an alias, or an imported namespace member is rejected during resolution with TPZ3015. This rejection precedes the immutable-root check. Data mutation and mutable local values follow the imported value rule.

An exported declaration publishes its resolved type, whether that type is annotated or inferred. Expand transparent type aliases before checking visibility. Every reachable record, enum, or newtype identity must be exported by its defining module. Check nested type components and type arguments recursively, including collections, structural records, unions, and function types. The rule covers function parameters and results, let and const bindings, type aliases, enum payloads, record fields, newtype bases, and exported protocol method parameters and results. A private alias whose expansion contains accessible types is accepted. A reachable private nominal type is rejected with TPZ3014 in the resolve phase. The primary location is the offending exported type reference when annotated, or the exported declaration's name when inferred.

Namespace visibility

An imported value is an immutable binding. The importing module cannot change its data through that binding. let mut local = imported receives an independent data value under collection value semantics. Changing the local leaves the exported value unchanged. Imported host resource handles, such as File, retain shared resource state.

A use item and a string or template module path are rejected with TPZ2008.

The forms export { name } and export import module are rejected with TPZ2009.